Method for restoring whiteness to yellowed nylon fabrics



U itc States atc'ri't' METHOD FOR RESTOG WHITENESS TO YELLOWED NYLON FABRICS Larry J. Barton, San Leandro, Calif., assignor, by mesne assignments, to The Clorox Company, Cincinnati, Ohio, a corporation of Ohio No Drawing. Application September 27, 1955 Serial No. 537,068

6 Claims. (Cl. 8-108) One of the problems that has arisen over the past few years has been that of white nylon fabrics age yellowing to the point that they become unsightly in appearance. The use of white nylon for nurses uniforms, waitresses garments, professional peoples jackets and similar types--including,shirts, underwear and stockings--has widely increased in popularity. These types of articles, if for nothing but appearance, should be maintained in a white and. sanitary appearing condition.

The age yellowingis the result of a combination of conditions such as exposure of these garments to the atmosphere in general, to the action of sunlight and particularly due to washing effects generally caused by the modern-day type of detergents. As time passes, the yellowing increases in amount to the point where eventually such yellow approaches a light brown in color. It

is quite evident that during this yellowing period, such- .garments become unsightly and are not fit to be used for the purposes for which they are intended.

A great deal of experimental work has been performed to devise some method to eliminate such yellow color and to bring back the fabric to its original whiteness. Substances such as potassium permanganate, hydrogen peroxide, sodium and other alkali metal hypochlorites, sodium sulfite, sodium bisulfite, sulfurous acid and sulfoxalate-formaldehyde salts have been used in an attempt to eliminate thisyellow color but with'no success. I

Various complex treatments have been suggested, such as the use of a detergent to wash the fabric first, followedby the use of 'a reducing agent and then followed by the use of an oxidizing agent. Whilesuch a complex formulation gives fairly good results, it requires a con siderable amount of time upon the part of the housewife and requires a combination of operations, such as rinsing between treatments; and does not offer a really satisfactory method of obtaining the end result desired.

' One type of product on the market at the present time t which aids in the overcoming of such yellow coloring are solutions of optical dyes or Blancophors.

Summarizing thisinvention, it is designed to overcome thetoregoingproblem, and has as its-objects,.among others, the provision of a quick, convenient and satisfactory method capable of being readily performed, for

v example, byany housewife quickly and accurately in herown home, using-a composition comprising economical materials which are found in practically every householdv orIwhich maybe quickly obtained at the nearest A These solutions do not remove the yellow, but due to their reflecgrocery store, and which will safely restore to their original whiteness age yellowed nylon fabrics or garments.

.7 agent together with a controlled amount of an acid,

preferably a weak organic acid, such as acetic, citric, malic or tartaric, to impart to the solution critical pH and available chlorine ranges, which will restore the whiteness and yet not damage the nylon.

Such solution will quickly and readily remove the yellow color, bringing the nylon fabric back to its original whiteness and will perform such operation without any undue deterioration to the fabric. For a practical household application, vinegar may be the source of acetic acid, while. lemon juice, orange juice or grapefruit juice may be the source of citric acid, and, consequently, may be employed for such purpose. Sodium hypochlorite, in the form of a 5.25% by weight aqueous solution is widely available and is consequently preferred as the bleaching agent in providing the available chlorine in the composition.

its pH (a measure ofhydrogen ion concentration). To

1.0 gallon of water, optimum results are obtained after adding 2.0 full tablespoons (one ounce) of a 5.25% by weight aqueous sodium hypochlorite'solution, together with 1.0 full teaspoon (Ms ounce) of household vinegar obtained in any grocery store, or lemon juice, orangev juice or grapefruit juice. The vinegar and citrus fruit juices contain approximately 5.0% by weight of the weak organic acid. The resultant solution will contain approximately 400 parts by weight per million of available chlorine and will have a pH ranging from approximately 8.00 to 8.30. A solution of approximately 400 parts by weight per million available chlorine made from a sodium hypochlorite solution and water alone would have a pH of approximately 9.30 to 9.70.

The 'vinegar'or citric acid containing fruit juices may vary inthe solution of 1.0 gallon of water and 2.0 tablespoonfuls of the 5.25 sodium hypochlorite solution, from as low as /2 teaspoonful, which will impart a pH range of approximately 8.50 to 8.70, to as high as 2.0 teaspoon- -fuls which will impart a pH ranging from 7.70 to 7.90.

Such solutions at a temperature of approximately 125 R, which is the approximate temperature of household warm washing water, will generally remove even the mostintense yellow from white'nylon immersed therein in 15- to 30, minutes. Even if it should be necessary to repeat such treatment, the fabric will not be adversely affected in tensile strength.

Based upon extensive experimentation, it has been determined that the lowering of the amount of the 5.25%

sodium hypochlorite solution, for instance to much below 110 tablespoonful per gallon of water with the preferred amount of acid, does not give any better whiteness, but .does have a deleterious effect upon the strength of the. fabric itself. This is believed so because 'too little of the hypochlorite results in too low a pH increased to much over4.0 tablespoonfuls with the same 1 which causes degradation of the nylon. v been determined from such experimentation that if the amount of the 5.25% sodium hypochlorite solution is preferred amount of acid, no better whitening is obtained; and.there is a decided weakening of the fabric strength which is believed due to too high a pH. 'If more of the acid is added, which has the elfect of lowering the pH,

again there is no increase in whitening capabilities, .but

It also has able chlorine content is too low, satisfactory whiten ing is not obtained while if the available chlorine content is too high, damage to the fibre results. The available chlorine content of the solution should, therefore, not be much below 200 parts by weight per million and should not substantially exceed 800 parts by weight per million, while the pH range should not vary too much from between 7.70 and 8.70 with the optimum results, as aforementioned, of 400 parts by weight per million available chlorine with a pH ranging between 8.00 and 8.30. Any proportions of the acid, hypochlorite and water may be employed to provide these ranges, depending on the concentrations of the acid and the hypochlorite employed, and also the volume of water, as it is immaterial what such concentrations or volume may be.

In this connection, other acids such as boric, oxalic, phosphoric, hydrochloric, nitric or sulfuric could be used under very carefully controlled conditions to provide the pH range indicated, but it is preferred to employ weak organic acids because the amount added to the nylon treating solution need not be so precisely controlled for providing the proper pH range, rendering their use more suitable by non-technical persons in a household. Of such weak organic acids, acetic and citric acid are most desirable because they are present, respectively, in vinegar and citrus fruit juice usually found in the ordinary household.

While an initial aqueous solution of 5.25% by weight sodium hypochlorite is preferred due to its ready availability in any grocery store, calcium hypochlorite, potassium hypochlorite, lithium hypochlorite or any of the organic powdered compounds can be utilized containing a chlorine radical which in the presence of an aqueous solution willdevelop available chlorine, so long as such nylon treating solution meets the required parts per million of available chlorine, together with the requirements covered by the pH range as described. Also, aspreviously mentioned, instead of vinegar or the' citric acid containing fruit juices, the weak organic acids themselves or other acids can be employed.

The actual treatment of the nylon fabric, which may be any of the fabrics available in stores in the form of garments or otherwise and varying from fine spun fabrics to woven wear, is quite simple. All that need be done is to soak the yellowed fabric in the treating solution for a suitable period of time which may vary from 15 to 40 minutes, depending on the extent of the yellowing and the temperature of the water, then remove the fabric and thoroughly rinse it in clean clear water,

preferably at room temperature but which may be Warm,

if so desired. Warm water is preferred forthe treating solution; the usual temperature of such water in household washing operations being approximately 125 F., and such temperature is preferred. The soaking should not exceed much over 40 minutes because too long a soaking at one time may weaken the fabric.

No rubbing of the nylon in the treating solution is necessary. The minimum time for the length of soaking is not critical because it is only necessary to allow the nylon to stand immersed for a period sufficient to remove the yellowing, but not long enoughlo cause damage to the fabric; and if the nylon has been soaked for a time insufficient to remove the yellow, it can be treated again. A minimum of 15 minutes of soaking temperature water because the action is slightly slower with cold water. However, room temperature or cold water can be employed. Real hot water in the order of 180 to 200 F. or boiling water may be utilized, but is not recommended because although whitening the fab ric more quickly, it may damage the same due to the heat alone.. In certain cases where the fabric has become highly yellowed, it may be necessary to repeat the treatment of the fabric.

After the solution is prepared for the treatment of the nylon, it should be employed relatively promptly, namely, within approximately 24 hours. This is so because the incorporation of the acid results in relatively rapid loss of available chlorine content; and the solution will not hold its available chlorine content for much over 24 hours.' Therefore, after preparation, the solution should be used promptly within an hour or two for best results; thesooner the better.

After the nylon has. been treated, it will be restored to. original whiteness, and will remain white for a period comparable to that of new nylonfabric before the treatment, namely, for about 3 to 4 months. Upon yellowing of the fabric again during usage after a treatment, the original whiteness can again be restored by further treatment with the solution.

The following example is illustrative of the preferred method and composition of the invention:

To 1.0 gallon of clean clear water in the neighborhood of F., add 2.0 tablespoonfuls (one ounce) of. a 5.25% by weight sodium hypochlorite solution, such as is commonly sold as a household bleach and disinfectant in grocery stores, and 1.0 teaspoonful /6 ounce) of household vinegar, such household vinegar being standard and.

containing approximately 5.0% by weight acetic acid. This solution is thoroughly mixed; and promptly after the mixing, the yellowed nylon fabric is immersed and allowed to soak or stand in the solution 15 minutes if only mildly yellowed, and 30 minutes it quite yellowed. At the end of such time, the fabric is separated from the solution by removal therefrom, and thoroughly rinsed clean of the solution in clean clear water at room temperature. pletely removed without any damage to the fabric. However, in certain instances where a high degree of yellow had occurred, it might be necessary to repeat this operanon.

GI claim:

1 1. The method of. restoring to whiteness age yellowed nylon garment fabric which consists essentially in the single whitening step of soaking such fabric for a period of about .15 to 40 minutes in an aqueous solution consist ing essentially of an hypochlorite and a weak organic acid ofthe group consisting of acetic acid and citric acid contained, respectively,inhousehold vinegar and citrus fruit juice, said acid being in an amountto provide a pH of said solution rangingfrom 7.70 to 8.70 and anavailable chloa rine content offrom'200 to800 parts per million, and

after such whitening step effecting separationbetween the and a weakorganic acid, said solution having a pH rang ing from 7.70 to 8.70 and an available chlorine content of from 200 to 800 parts per million, and after such period rinsing the solution fromthe fabric.

3. The method of claim 2, in which the hypochlorite is sodium hypochlorite, and the acid is of the group consisting of acetic and citric acid contained, respectively, in household vinegar and citrus fruit juice.

4. The method of claim, 2, in which the hypochlorite is'sodium hypochlorite in an amount which normally provides an available chlorine content of 400 parts per million The yellowing will inmost instances be com age yellowed and a pH between 9.30 and 9.70 in water solution, and in which the acid is of the group consisting of acetic acid and citric acid, said acid being present in an amount in relation to the amount of hypochlorite to impart a pH of between 8.00 and 8.30 to said. solution containing said available chlorine content.

5. The method of claim 2, wherein said hypochlorite is a 5.25% by weight sodium hypochlorite solution present in the proportion of 1.0 to 4.0 tablespoonfuls of said solution per 1.0 gallon. of water, and wherein said acid consists of an organic acid of the group consisting of acetic and citric acid contained, respectively, in /2 to 2 teaspoonfuls of household vinegar and citrus fruit juice per gallon of water.

6. The method of claim 1 in which the amount of said sodium hypochlorite solution is 2.0 tablespoonfuls, and the amount of said acid is 1.0 teaspoonful.

References Cited inthe file of this patent UNITED STATES PATENTS OTHER REFERENCES Ridge et al): J. Textile Institute, May 1942, pages 162164.

I U. s. DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 2,830,868 Larry J, Barton April 1.5, 1958 pears .in the printed specification It is hereby certified that error ap rrection and that the said Letter of the above numbered patent requiring co Patent should read as corrected below.

Column, line 1, for the claim reference numeral "1" read 5 Signed and sealed this 17th day of June 1958.

(SEAL) Attest:

R MINE. ROBERT C. WATSON Attesting Officer Conmissioner of Patent U. 8. DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,830,868 Larry J. Barton It is hereby certified that error appears .in the printed specification of the above numbered patent requiring correction and that the said Letters April 15 1958 v Patent should read as corrected below.

Column 6, line I, for the claim reference numeral "1'' read 5 Signed and sealed this 17th day of June 1958.

(SEAL) Atfiest:

KARL AXLINE ROBERT c. wATsm/ Attesting Officer Gon'missioner of Patent) 

1. THE METHOD OF RESTORING TO WHITENESS AGE YELLOWED NYLON GARMENT FABRIC WHICH CONSISTS ESSENTIALLY IN THE SINGLE WHITENING STEP OF SOAKING SUCH FABRIC FOR A PERIOD OF ABOUT 15 TO 40 MINUTES IN AN AQUEOUS SOLUTION CONSISTING ESSENTIALLY OF AN HYPOCHLORITE AND A WEAK ORGANIC ACID OF THE GROUP CONSISTING OF ACETIC ACID AND CITRIC ACID CONTAINED, RESPECTIVELY, IN HOUSHOLD VINEGAR AND CITRUS FRUIT JUICE, SAID ACID BEING IN AN AMOUNT TO PROVIDE A PH OF SAID SOLUTION RANGING FROM 7.70 TO 8.70 AND AN AVAILABLE CHLORINE CONTENT OF FROM 200 TO 800 PARTS PER MILLION, AND AFTER SUCH WHITENING STEP EFFECTING SEPARATION BETWEEN THE GARMENT AND SAID SOLUTION. 